1. Field of the Invention
The present invention relates to an image correction apparatus and an image correction method adapted to correct an image provided from an imaging device, e.g., an imaging device mounted to a vehicle to image a periphery of the vehicle. The present invention also relates to a method of making a transformation map for the image correction apparatus and method.
2. Description of Related Art
A vehicle periphery displaying apparatus is known. For example, JP-H10-257482A discloses a vehicle periphery displaying apparatus that simultaneously displays images of a left side, a right side and a rear side of the vehicle on a liquid crystal display panel. This vehicle periphery displaying apparatus takes a vehicle right side image and a vehicle left side image by using CCD (charge coupled device) cameras mounted in the vicinity of a right door mirror and a left door mirror of the vehicle. The vehicle periphery displaying apparatus takes a vehicle rear side image by using a CCD camera mounted to a rear part of the vehicle. Then, respective points of infinity of the three images (i.e., the vehicle right, left and rear side images) are made match each other, and thereby one point of infinity is set. From the three images, an image viewed from a single virtual viewpoint is synthesized.
The inventors of the present application have found that a conventional technique involves the following disadvantage, discussion on which will be given below as a related art.
When the points of infinity of the three images are made match each other in the image synthesis, a white line on a road and the like can be displayed continuously between the vehicle right/left side image and the vehicle rear side image.
Each of the CCD cameras for taking the vehicle right, left and rear side images typically has an optical axis that is set inclined downward with respect to a direction parallel to the road surface. Hence, a three dimensional (3D) object is displayed on the vehicle right/left side image and the rear side image so that the displayed 3D object has discontinuity between the vehicle right/left side image and the rear side image, resulting in incomprehensible display.
The above point will be more specifically described with reference to the drawings. An assumed situation is as follows. As shown in FIG. 4, a CCD camera is mounted to a rear part of a vehicle to image a rear side of the vehicle. On a right side and a left side on a road behind the vehicle, poles with a height of 1.5 m are provided at 2 m intervals. A distance between the CCD camera and a closest pole in a vehicle width direction is 2.6 m. The CCD camera has an angle of view of 130 degrees in the vehicle width direction.
In the above situation, if an optical axis of the CCD camera is parallel to the road surface, the poles provided on the right side and the left side of the road is imaged so as to extend in an vertical direction on the camera image (i.e., an image taken with the CCD camera), as shown in FIGS. 14A and 14B. Further, as shown in FIGS. 14A and 14B, even if the installation height of the CCD camera is changed, as long as the optical axis of the CCD camera is parallel to the road surface, the display object that should be displayed in the vertical direction is not inclined with respect to the vertical direction on the image taken with the CCD camera.
However, a CCD camera mounted to a vehicle is typically used to monitor a situation of the vicinity of the vehicle. Thus, a CCD camera is typically mounted to a vehicle so that an optical axis of the CCD camera is not parallel to the road surface but inclined downward with respect to a direction parallel to the road surface. If the optical axis of the CCD camera is inclined downward by 25 degrees with respect to the direction parallel to the road surface for example, the poles on the left side and the right side of the road are displayed so as to be inclined with respect to the vertical direction, as shown in FIGS. 15A and 15B. Angle of the inclination is larger with increasing distance from the center of the image.
Since a display object closer to an edge of the image has a larger angle of the inclination and a larger distortion, the display object closer to the edge is poorly viewable on the camera image. Furthermore, when multiple images in each which a display object closer to the edge of the image has a larger inclination are joined to each other and when the joined images are displayed, the direction of the inclination of the same display object can vary among the multiple images. The display object displayed at the border between the multiple images is poorly viewable in particular.